Acetaminophen and tramadol are commonly used analgesics, and have been used alone or in combination for a number of years. An immediate release tablet composition comprising tramadol and acetaminophen, and its use, has been described, for example, in U.S. Pat. No. 5,336,691, which reissued as U.S. Pat. No. RE39,221. Immediate release compositions have been available commercially under the tradename Ultracet®, which usually are administered in adults every four to six hours. Ultracet® has been used successfully in acute pain management for many years.
Nevertheless, there is a desire to produce sustained release formulations containing both tramadol and acetaminophen to facilitate better pain management and patient convenience and quality of life. It is contemplated that sustained release products will provide improved patient convenience as they would not require remembering to take, and then taking, as many doses over a twelve hour period. This feature has the added benefit of avoiding break-through pain which may occur if a repeat dose of an immediate release product is omitted or mis-timed. Furthermore, it is believed that sustained release products will improve quality of life since they generally reduce fluctuations in plasma concentrations, potentially providing more consistent analgesia.
In general, because Acetaminophen is a low potency drug requiring large doses to be administered for effective and prolonged analgesia and because the distal regions of the gastrointestinal tract such as the colon have a small surface area for absorption as compared to the proximal small bowel, it is believed that it is difficult to administer acetaminophen in a single dosage to achieve sufficiently high plasma concentrations to achieve sustained analgesia for more than eight hours. A number of sustained release formulations for the delivery of a combination of acetaminophen and tramadol have been described, for example, in U.S. Pat. No. 7,374,781 and U.S. Patent Publication No. US2003/0092724 A1. No sustained release formulations containing both tramadol and acetaminophen, however, have been approved to date in the U.S. or Europe.
As a result, there is still a need for compositions that permit the delivery of acetaminophen and tramadol over prolonged periods of time, for example, at least about twelve hours, to facilitate pain management over that period of time.